Spring Boot Tutorial 0/110 lessons ~6 min read Lesson 71“Production-grade backends”

Circuit Breaker

When a downstream service is failing, hammering it makes everything worse.

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Focus

2 guided sections

Practice signal

Examples included

Career prep

Foundation builder

Introduction

When a downstream service is failing, hammering it makes everything worse. A circuit breaker trips after N failures, fails fast for a cool-down period, then probes — protecting your service and the dependency.

Informative example

Resilience4j with Spring Boot:

# pom.xml
<dependency>
  <groupId>io.github.resilience4j</groupId>
  <artifactId>resilience4j-spring-boot3</artifactId>
</dependency>

# application.yml
resilience4j.circuitbreaker:
  instances:
    pricing:
      slidingWindowSize: 20
      failureRateThreshold: 50
      waitDurationInOpenState: 30s
      permittedNumberOfCallsInHalfOpenState: 5

@Service @RequiredArgsConstructor
public class PricingFacade {
  private final PricingClient client;

  @CircuitBreaker(name = "pricing", fallbackMethod = "fallback")
  @Retry(name = "pricing")
  @TimeLimiter(name = "pricing")
  public CompletableFuture<Quote> quote(List<LineItem> items) { return client.quote(items); }

  CompletableFuture<Quote> fallback(List<LineItem> items, Throwable t) {
    return CompletableFuture.completedFuture(Quote.cached(items));
  }
}

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